Dehydration of organic materials is common in the food processing and the medicinal herb industry. It may be done in order to preserve the products for storage, for example fruits and vegetables, the dehydrated products being later rehydrated for consumption. Dehydration may also be done to create a product that is used in the dehydrated form, for example dried herbs and various kinds of chips. Conventional methods of dehydrating such materials include air-drying and freeze-drying. Both of these drying methods have their limitations. In general terms, air-drying is slow and freeze-drying is expensive, and both methods tend to degrade the appearance and texture of the products.
It is also known in the art to dehydrate foods and plant materials by microwave vacuum dehydration. Examples of this in the patent literature include: U.S. Pat. No. 4,664,924 Sugisawa et al.; U.S. Pat. No. 6,128,831 Durance et al.; U.S. Pat. No. 5,956,865 Durance et al.; U.S. Pat. No. 4,389,794 Bitterly; U.S. Pat. No. 4,809,596 Akutsu et al.; U.S. Pat. No. 4,882,851 Wennerstrum et al.; and WO 021103407 Al Radas et al. Microwave vacuum-drying is a rapid method that can yield products with improved quality compared to air-dried and freeze-dried products. Because the drying is done under reduced pressure, the boiling point of water and the oxygen content of the atmosphere is lowered, so food or medicinal components sensitive to oxidation and thermal degradation can be retained to a higher degree than by air-drying. The drying process is also much faster than air- and freeze-drying. The present invention is directed to improvements in the art of microwave vacuum-drying.